ros node does not seem to do anything

Question

I have the following code for the ros turtlesim:

 #include <ros/ros.h>
#include <std_msgs/String.h> 
#include "geometry_msgs/Twist.h"
#include <stdio.h>     
#include <stdlib.h>     
#include <time.h>       
void disruptcb(geometry_msgs::Twist msg) {
    ros::NodeHandle pubHandle;
    ros::Publisher publisher = pubHandle.advertise<geometry_msgs::Twist>("turtle1/cmd_vel", 1000);
    ros::Rate loop_rate(2);

        double dist1=(rand()%100);
        double dist2=(rand()%100);
        std::cout<<dist1<<std::endl;
        dist1=dist1;
        dist2=dist2; 
        msg.linear.x+=dist1;
        msg.angular.z+=dist2; 
        std::cout<<msg<<std::endl;
        ROS_INFO("hello" );
        publisher.publish(msg);

}
int main(int argc,char** argv){
    srand(time(NULL));
    ros::init(argc,argv, "things_going_wrong");
    ros::NodeHandle nh;
    ros::Subscriber sub = nh.subscribe("/ros_1/cmd_vel",1000,&disruptcb);
    ros::spin(); 
}

the idea behind this code is to introduce a random error to then practice error recovery in my code but this node does not appear to do anything at all. I do know that my other nodes are running but this one just doesn't appear to do anything, it doesn't exit it just hangs. Anybody know how to fix this?

Answer 1

I have tried your code. When publishing a message on "/ros_1/cmd_vel" your disruptcb will be called.

rostopic pub /ros_1/cmd_vel geometry_msgs/Twist '{linear: {x: 1, y: 2, z: 3}, angular: {x: 1,y: 2,z: 3}}'

But I can't connect to your outcome message "turtle1/cmd_vel". Try to advertise it inside the main function:

ros::Publisher* publisher;
void disruptcb(geometry_msgs::Twist msg) {
    ...
    publisher->publish(msg);
}                   
int main(int argc,char** argv){
    ros::init(argc,argv, "things_going_wrong");
    ros::NodeHandle nh;
    ros::Subscriber sub = nh.subscribe("/ros_1/cmd_vel",1000,&disruptcb);
    publisher = new ros::Publisher(nh.advertise<geometry_msgs::Twist>("turtle1/cmd_vel", 1000));
    ros::spin();
    delete publisher;
}

Then outcome message will also be observed:

rostopic echo /turtle1/cmd_vel